Synthesis and time-resolved absorption spectra of 1,3,3,5,2'-pentamethylspiro[indolinnaphthooxazine

Abstract

The title compound 1,3,3,5,2'-pentamethylspirooxazine (I) is synthesized and identified by 1R, 1H NMR and elemental analysis. The time-resolved transient absorption spectra of I are investigated by nanosecond laser flash photolysis. The photolysis of I in solution excited by 248 nm laser pulse results in two different colored species. One of them is a short-lived species (CT intermediate), which has two absorption maxima at 440 and 640 nm in acetonitrile, and 450 and 640 nm in cyclohexane. The corresponding lifetimes are 12 and 0.8 us, respectively. The absorption spectra of CT intermediate are not influenced by solvent polarity. This fact indicates that the structure of CT is between the zwitterionic and quinoidal ones. The much longer lifetime of CT in acetonitrile than in cyclohexane is due to the electron donating effect of methyl in position 5 of indolino ring. The long-lived colored species (>>80 us) proves a planar photomerocyanine (PMC) structure, whose absorption spectra in acetonitrile and cyclohexane show the absorption maxima at 640 and 600nm, respectively.